Department of Environmental Science and Engineering, Tsinghua University, Beijing 100084, PR China.
Environ Sci Technol. 2010 Dec 15;44(24):9590-6. doi: 10.1021/es102692b. Epub 2010 Nov 18.
CeO(2)/TiO(2) and CeO(2)-WO(3)/TiO(2) catalysts prepared by impregnation method assisted with ultrasonic energy were investigated on the selective catalytic reduction (SCR) of NO(x) (NO and NO(2)) by NH(3). The catalytic activity of 10% CeO(2)/TiO(2) (CeTi) was greatly enhanced by the addition of 6% WO(3) in the broad temperature range of 200-500 °C, the promotion mechanism was proposed on basis of the results of in situ diffuse reflectance infrared transform spectroscopy (DRIFT). When NH(3) was introduced into both catalysts preadsorbed with NO + O(2), SCR would not proceed except for the reaction between NO(2) and ammonia. For CeO(2)/TiO(2) catalysts, coordinated NH(3) linked to Lewis acid sites were the main adsorbed ammonia species. When NO + O(2) was introduced, all the ammonia species consumed rapidly, indicating that these species could react with NO(x) effectively. Two different reaction routes, L-H mechanism at low temperature (<200 °C) and E-R mechanism at high temperatures (>200 °C), were presented for SCR reaction over CeO(2)/TiO(2) catalyst. For CeO(2)-WO(3)/TiO(2) catalysts, the Lewis acid sites on Ce(4+) state could be converted to Brønsted acid sites due to the unsaturated coordination of Ce(n+) and W(n+) ions. When NO + O(2) was introduced, the reaction proceeded more quickly than that on CeO(2)/TiO(2). The reaction route mainly followed E-R mechanism in the temperature range investigated (150-350 °C) over CeO(2)-WO(3)/TiO(2) catalysts. Tungstation was beneficial for the formation of Ce(3+), which would influence the active sites of the catalyst and further change the mechanisms of SCR reaction. In this way, the cooperation of tungstation and the presence of Ce(3+) state resulted in the better activity of CeO(2)-WO(3)/TiO(2) compared to that of CeO(2)/TiO(2).
采用超声辅助浸渍法制备了 CeO(2)/TiO(2) 和 CeO(2)-WO(3)/TiO(2) 催化剂，并研究了它们在 NH(3) 选择性催化还原（SCR）NO(x)（NO 和 NO(2)）中的催化活性。在 200-500°C 的宽温度范围内，添加 6%WO(3)可大大提高 10%CeO(2)/TiO(2)（CeTi）的催化活性，其促进机制是基于原位漫反射红外变换光谱（DRIFT）的结果提出的。当 NH(3) 被引入到预吸附了 NO + O(2)的两种催化剂中时，除了 NO(2)和氨之间的反应之外，SCR 不会进行。对于 CeO(2)/TiO(2)催化剂，与路易斯酸位配位的 NH(3)是主要的吸附氨物种。当引入 NO + O(2)时，所有的氨物种都迅速消耗，表明这些物种可以有效地与 NO(x)反应。在 CeO(2)/TiO(2)催化剂上，SCR 反应呈现出两种不同的反应途径，低温（<200°C）下的 L-H 机制和高温（>200°C）下的 E-R 机制。对于 CeO(2)-WO(3)/TiO(2)催化剂，Ce(4+)态上的路易斯酸位由于 Ce(n+)和 W(n+)离子的不饱和配位可以转化为布朗斯台德酸位。当引入 NO + O(2)时，反应速度比在 CeO(2)/TiO(2)上更快。在研究的温度范围内（150-350°C），CeO(2)-WO(3)/TiO(2)催化剂上的反应主要遵循 E-R 机制。钨酸盐有利于 Ce(3+)的形成，这会影响催化剂的活性位，并进一步改变 SCR 反应的机制。通过这种方式，钨酸盐的协同作用和 Ce(3+)态的存在使得 CeO(2)-WO(3)/TiO(2)的活性优于 CeO(2)/TiO(2)。
